1. Field of the Invention
The present invention relates to a process whereby the flyash removed from exhaust gases of devices burning organic fuel is separated into usable components for recycling, and waste components for disposal. The process utilizes size and density classifiers to separate carbon rich fractions for reinjection or resale as carbon product. In the case where mineral sorbents are present in the flyash the present invention can be configured to separate the reacted and unreacted sorbent from the flyash to minimize costs for disposal of hazardous materials. The present invention processes particulate at any time after collection into an ash hopper.
2. Description of Related Art
Mechanical separators, such as multiclones and screens, have previously been used to remove both flyash and unburned carbon from the exhaust gases of boilers and other fuel burning devices. Their primary purpose being the removal of solids from exhaust gases for the purpose of controlling air pollution. In many cases where combustion is incomplete due to nitrogen oxide control for environmental reasons, much of what is removed are particles of high carbon content that are suitable for recombustion, thus saving on fuel costs.
Some previous systems, such as the invention disclosed in U.S. Pat. No. 2,750,903 to Miller et al, recover carbon rich fractions from exhaust gases and reinject them for combustion. Another problem encountered is the disposal of flyash that has been treated with a sorbent material, such as lime, to control SOx and NOx found in the exhaust gases.
Typically, the sorbent material will be introduced into the combustion vessel, a separate vessel, or the associated duct work. In the case of sorbent use the ratio of sorbent to carbon rich particles in the exhaust particulate is extremely high, typically about 150:1, so carbon recovery is not a large concern. If allowed to collect along with the flyash the sorbent/flyash mixture becomes a hazardous material because of its high ph level. As a hazardous material the mixture must be disposed of properly, and at great expense.
Previous inventions have attempted to separate the sorbent particles from the flyash particles. However, the prior systems operate on the whole exhaust gas stream. This necessitates large, costly equipment designed integrally with the boiler. While the subject of U.S. Pat. No. 4,669,397 to Galagana et al can act on particulate matter subsequent to combustion and collection, its concern is the removal of ferrous material from the exhaust particulate. Galagana does not deal with carbon reinjection or sorbent recovery.
In summary, many inventions, such as the cited references, have addressed the problems of separating carbon rich particles and sorbent particles from the exhaust of the combustion of organic fuel. These systems have all operated on the entire gas stream as it exits the combustion vessel. This requires expensive equipment integral to the combustion system. These systems have also utilized, to varying extent, specialized methods of size and density particle separation also at a great expense.